There is known a solvent recovery apparatus comprising:
an adsorption tower having a gas adsorption element; PA1 a gas supply pipe for supplying solvent-containing gas to be treated; PA1 a steam supply pipe for supplying steam to be used for solvent removal; PA1 a solvent recovery pipe for recovering a removed solvent; PA1 the gas supply pipe, the steam supply pipe and the solvent recovery pipe being connected to the adsorption tower; PA1 a condenser for cooling and liquefying gas containing a solvent removed from the gas adsorption element; and PA1 a specific-gravity separating unit for recovering a liquefied solvent as separated from water by specific gravity; PA1 the condenser and the specific-gravity separating unit being connected to the solvent recovery pipe.
When conventionally separating and recovering a solvent from solvent-containing gas to be treated with the use of the solvent recovery apparatus of the type above-mentioned, solvent-containing gas exhausted from the adsorption tower by the supply of steam is supplied to the condenser by which both the steam and the solvent are liquefied, and the resultant mixture of water and the liquefied solvent is then supplied to the specific-gravity separating unit in which only the liquefied solvent, having been separated from the water by specific gravity, is recovered.
For a solvent, such as fluorocarbons, which has a specific gravity greater than that of water, the specific-gravity separating unit is conventionally arranged as shown in FIG. 9 (a). More specifically, connected to the top of a lateral side of a casing 101 is a supply pipe 102 which forms a part of the solvent recovery pipe and which supplies a liquid mixture of water W and a solvent L liquefied by the condenser. The casing 101 is provided at a portion thereof, apart from the portion thereof connected to the supply pipe 102, with a partition wall 103 to be used for separation of the liquid mixture by specific gravity. A water receiving portion 104 for recovering the water W by overflow is formed at the upper portion of the partition wall 103 to a side of the supply pipe 102. The water receiving portion 104 has a drain port 105. An outlet port 106 for the liquefied solvent L is formed at the opposite side of the water receiving portion 104 with respect to the partition wall 103. The liquid mixture of the water W and the liquefied solvent L is supplied into the casing 101 and, as a result of the difference in their specific gravity, the water W and the liquefied solvent L separate respectively into an upper layer and a lower layer so that the water W in the upper layer is recovered through the water receiving portion 104 and the drain port 105, and the liquefied solvent L in the lower layer passes below the lower end of the partition wall 103 and is recovered through the outlet port 106.
For a solvent L having a specific gravity which is smaller than that of water, provision is made such that the water W and the liquefied solvent L are respectively discharged from the outlet port 106 and the drain port 105.
In the solvent recovery apparatus above-mentioned, when steam is supplied for removing a solvent adsorbed by the gas adsorption element of the adsorption tower, the air present in the adsorption tower is suddenly expanded as it is heated, thereby to increase the internal pressure in the adsorption tower. Further, the pressure of the steam at the time the same is supplied, is added to the internal pressure. Accordingly, the internal pressure in the casing 101 of the specific-gravity separating unit is suddenly increased. When the internal pressure in the casing 101 is suddenly increased, the liquid level therein is lowered as shown in FIG. 9 (b). This causes the level of the water W which has separated into the upper layer to be lowered below the lower end of the partition wall 103. Thus, the water W accidentally flows into the space at the side of the outlet port 106. Accordingly, the liquefied solvent L which is recovered is contaminated with the water W, so that the liquefied solvent L thus recovered cannot be reused.
Further, the gas phase in the condenser contains a solvent in an amount which corresponds to a saturated vapor pressure at the cooling temperature of the condenser. The concentration of the solvent is considerably higher than that of the solvent contained in gas supplied from the gas supply pipe. At the time of solvent removal where the pressure is suddenly increased, the high-concentration solvent present in the gas phase in the condenser and gas containing a solvent removed from the gas adsorption element flow, without being condensed and liquefied by the condenser, into the drain port 105, and leak to the outside. This decreases the efficiency of solvent recovery. Such leakage of solvent-containing gas is considerable particularly in a solvent recovery apparatus of the one-tower type having one adsorption tower in which solvent adsorption and solvent removal are alternately carried out.